后悔 + 没 + Verb / 后悔 + Verb + 了
后悔 (hòuhuǐ) means "to regret" or "to feel remorse" and describes the feeling of wishing one had acted differently. It is often followed by 没 + Verb to express regret about not having done something.
我真后悔没听你的话。
wǒ zhēn hòuhuǐ méi tīng nǐ de huà.
I really regret not listening to you.
她后悔当初没有好好学英语。
tā hòuhuǐ dāngchū méiyǒu hǎohǎo xué yīngyǔ.
She regrets not having studied English well back then.
你现在不努力,将来会后悔的。
Nǐ xiànzài bù nǔlì, jiānglái huì hòuhuǐ de.
If you don't work hard now, you'll regret it in the future.